Particle Physics and the mysteries
of the early Universe
Cristina Lazzeroni
Royal Society University Fellow
University of Birmingham
Over 12 billion years ago, the Big Bang gave birth to the
Universe, creating space, time, energy and matter.
To understand the laws of the universe, particle physicists
want to recreate conditions of less of billionth of second
after the Big Bang
100 million x Sun’s Temperature
Use
accelerators !
Particles accelerated to speed of light :
E=
2
Mc
Protons smashing together can produce all sorts
of particles, seen in the earliest moments of the universe
E = h
h = Plank constant
Particle-wave equivalence
Large Hadron Collider (LHC)
proton=hadron
27 km ring,
French-Swiss
boarder
magnets cooled to
1.9 K, colder than
outer space
Protons,
accelerated by 7
trillion volts, travel
at 0.999999991
speed of light and
smash together
600 million
times/sec
Beam spot
needle eye=0.3 mm diameter
beam = 0.03 mm diameter at
focus
The ‘Large Hadron Collider’ accelerates 2800 bunches,
1011 protons per bunch, at 7 TeV
This corresponds to:
350 MJ stored energy per
proton beam
= Kinetic energy of 1200 elephants
running at 25 mph
= Kinetic energy of family car
travelling at 1000 mph
= Kinetic energy of fully loaded Airbus
A320 at landing speed
= Enough energy to melt 550 kg copper
TOTAL ENERGY STORED in LHC superconducting
magnets: 10 GJ = “An avalanche”
(10000 t of snow, sliding down 100 m)
Rutherford’s Experiment in 1909
Expected:
 particle
Found:
 particle
New model of atom:
 particle
nucleus
electron
size:
Nucleus
Fly
=
Atom
Cathedral
‘like a fly in a cathedral’
cake tin, football,
ping pong balls
Ordinary matter is made of
fermions, held together by bosons
matter particle
force particle
Photons and gluons are ripples in the
(EM, strong) fields - quantum fields
Z,W : Weak force carriers
Overall there are
6 quarks, 6 leptons, 4 force carriers
e m t e m
. . .
t
W
u d s
c
b
top quark
Z
All nice, simple, understood ?!
There should be something (new particle)
in the universe that gives mass to all particles
Higgs Particles
e
x
x
W
t
x
x
x
x
x x
x x x
x
x
Mass is really a measure of how
difficult it is to accelerate an
object (F=ma)
Higgs field :
particle mass is a
measure of the
resistance to
movements through
this field
Higgs field magnetic field
Buridan’s Donkey
Photon, W+, W- massless
meta-stable
Photon massless
W+,W- massive
asymmetric
The “Mexican hat” :
radial symmetry
A ball at the top of the
‘hat’ can fall down in
any direction, all
equally probable.
When it does fall, a
particular direction is
chosen and the
symmetry is broken
The interesting events are very rare:
1 in 100,000,000,000 (1 followed by 11 zeros)
Equivalent to looking for one particular grain
in 2.5 million kg of rice
Higgs events are
rare
Cambridge, 1928 :
Dirac predicted the existence
of the positron e+, same mass
but opposite charge to eQuantum
Mechanics
i 
m
Special
Relativity

 m  mc   0
The Dirac Equation
Since then, many observations done but
mechanism/origin not yet clear
Matter and Anti-matter
Equal quantities of Matter and
Anti-matter should have been
produced in the Big Bang,
then annihilated each other
leaving just radiation
Escher images
Antimatter in the story of
TM & © 2009 Columbia Pictures Industries, Inc. All Rights Reserved.
In the Angels and
Demons story, the bad
guys go to a laboratory
called “CERN”.
They steal half a gram of
antimatter in a canister,
which they then take to
Rome to use as a bomb.
TM & © 2009 Columbia Pictures Industries, Inc. All Rights Reserved.
A feather weigths about ½ gram.
If We Could Accumulate It
If we had some means to
accumulate half a gram
and
if we could put it in a
container and
if we could transport it safely
to another site,
it would indeed be a
powerful bomb as in
TM & © 2009 Columbia Pictures Industries,
Inc. All Rights Reserved.
How Long to Get Half a Gram?
All the antimatter produced in
accelerators annihilates within
a fraction of a second.
If LHC could somehow
accumulate all the
antimatter it produced,
it would take 10 million
years to get ½ a gram of
antimatter
Supersymmetry: symmetry between types
of particles.
Every observed particle has a superpartner,
just too massive to have been already seen
How many spacetime dimensions? No reasons why
they should be 3 ... apart from observational reasons !
New dimensions can be small
Or impossible to detect :
Particles would become
extended objects
How are particles detected?
See our exhibition of working
detectors, LHC data taking and
many other activities,
including a new computer game !
World’s most massive
“onion” structure to
capture the particles
ATLAS Control Room, first beams, 20 November 2009
26
Max peak luminosity: L~1.6 x 1030 cm-2s-1
 average number of pp interactions per bunch-crossing: up to 1.3
 “pile-up” (~40% of the events have > 1 pp interaction per crossing)
Event with 4 pp interactions in the same bunch-crossing
~ 10-45 tracks with pT >150 MeV per vertex
Vertex z-positions : −3.2, −2.3, 0.5, 1.9 cm (vertex resolution better than ~200 μm)
Integrated luminosity vs time
(from first √s =7 TeV collisions on 30 March 2010 to beginning of ICHEP on 22 July)
(stable beams)
2.55 TeV mass
di-jet event
1st top-quark
candidate
1st W
1st Z
28
First searches for New Physics
29
Exciting times ahead !
Stay tuned and ...
be prepared for surprises !
Questions ?
And don’t forget the exhibition in the Bridge Study room !!
Spares
LHC Magnets store even more energy
•
•
•
•
1232 superconducting Dipoles,1.9 K, 8.33 Tesla
~400 superconducting Quadrupoles
~6000 superconducting corrector magnets
TOTAL ENERGY STORED in LHC superconducting magnets:
– 10 GJ = “An avalanche”
(10000 t of snow, sliding down
100 m)
Benefits
First, the new knowledge.
Also, the technology is pushed to the limits
and produces many practical applications
Most of the 17000 particle accelerators are
used in medicine for cancer treatment
Particle detectors are used in medical imaging
Then the computing :
the world wide web !
And soon the GRID
Physicists think that with very high energy beams
forces start to behave the same
as if there is just one force, not several forces
“Do all the
forces
become one ?”
• Primary cosmic ray in
upper atmosphere
• Collision with nucleus
• Initiates “cascade”
– Secondary cosmic rays
(pions that decay into muons,
electrons and neutrinos)
– Higher energy primary
• larger secondary shower
• Time dilation effects:
muons arrive at ground level
The Spark Chamber is a triggered device
Scintillation
counter S1
Particle
track
Photo-tube 1
HV Supply
Delay
(cables)
Trigger Unit
S2
Photo-tube 2
Coincidence
Unit
Detecting Particles
•Only 1 event / second
•Photos scanned by
hand
•No selection on events
Used Bubble
Chambers up to
1970s
How does the presence of matter change space and time?
It bends like a rubber sheet
It makes time go slower
the Universe was born with
equal amounts of matter and antimatter
CP violation :
t  0
(and B violation and
phase transitions)
the Universe contains
slightly more matter than antimatter
t ~ 1 m sec
Particles and anti-particles annihilate :
the Universe contains only matter
(and lots of photons)
t ~ 1 sec
The Quark-Gluon Plasma
 Strong Force: how does it generate 98% of the mass of
nuclear matter? why are there no free quarks?
 unlock the secrets of the primordial state of matter, the
Quark-Gluon Plasma, which would have existed up until about
10 millionths of a second after the Big Bang, and could be
created in the core of collapsing neutron stars
Normal hadronic matter
At extreme temperatures
and/or densities hadronic
matter ‘melts’ into a plasma of
free quarks and gluons.
How to Make a QGP
• Need very high energy
densities
• Create sub-atomic volumes of
hot, dense matter similar to
conditions 10-6s after Big
Bang
• Fireball must live long enough
for phase transition to take
place
• Collide lead ions (lead
nuclei) at highest energies
The Fireball
• Temperature of our fireball ~
1013K i.e. > 1,000,000 times
the temp of centre of Sun.
• Density ~ Great Pyramids
crushed to the size of a pinhead – similar to neutron
star densities (but much
hotter!)
T ~ 15,000,000 K
What Happens ?
• Energy is converted
into many quarks,
anti-quarks and
gluons.
• QGP lasts for about
10-22 seconds
• Then thousands of
particles are
produced
We have to study the QGP from this!
Only a small fraction of the total is ordinary
matter that we know
Feynman diagrams
Trees
Penguins
We are lucky because…
Immediately after the Big Bang,
the matter and antimatter… were NOT exactly equal
10,000,000,001
10,000,000,000
Matter
Antimatter
Notice
The Great Annihilation followed !!!
46
radioactive decays
How stars generate energy
Weak Force
Enrico Fermi
(1901 - 1954)
holding proton, nucleus
Strong Force
gluons
Size of nuclei is set by strength of strong force
Mexican hat: angular symmetry
Photon, W+, W- massless
meta-stable
Photon massless
W+,W- massive
asymmetric